This invention relates in general to firearms and deals more particularly with an improved pressure relief mechanism for a gas operated auto loading firearm. More specifically, the present invention is concerned with an improved automatic gas pressure control system for an auto loading shotgun which will accommodate any 2 or 3 inch commercial ammunition. The ammunition used with such a gun may be lead or steel shot, buckshot or slugs.
Heretofore, various gas relief mechanisms have been provided for auto loading firearms. An example of such a gas relief system is found in U.S. Pat. No. 4,901,623 to Lee for Compensating Device For Gas Actuated Firearms, assigned to the assignee of the present invention. The Lee compensating device is designed primarily for use on a gas operated auto loading shotgun loaded from a magazine tube and vents gases of explosion from a gas cylinder and in a forward direction or toward the muzzle end of the gun when gas pressure within the gas cylinder, which operates the action, exceeds a predetermined magnitude. The Lee device includes a rigid annular valve element encircling the magazine tube and supported by a plurality of parallel guide members or rods for axial movement along the guide members and toward and away from a complementary annular valve seat defined by the gas cylinder. Springs associated with the guide members bias the valve element toward and into seating engagement with the valve seat to form a closure for one or more vent ports which communicate with the interior of the gas cylinder and open through the valve seat. Preferably, the Lee device has at least three equangularly spaced apart vent ports which assure smooth axial movement of the valve element along and relative to the guide members without binding in response to the escape of gas under pressure from the gas cylinder. While the Lee compensating device provides satisfactory venting to control gas cylinder pressure, it has a large number of parts and is relatively expensive to manufacturer.
Accordingly, it is the general aim of the present invention to provide an improved forwardly vented gas pressure relief system for a firearm which enables a wide range of ammunition to be used in the firearm without requiring barrel change or adjustment of the system and which reduces the number of parts required to make such a system.